1. Field of the Invention
This invention relates generally to an apparatus for sensing the condition of a bearing and in particular to a transducer sensor for monitoring the condition of a trunnion bearing which supports a basic oxygen furnace vessel.
Prior Art
Bearing mounted rotatable shafts have utility in a variety of heavy equipment operations. During normal operation, such a rotatable shaft should rotate about a relatively stationary axis. Continued operation of heavy equipment can cause the bearing to wear and ultimately fail. The damage caused by such failure can be severe especially when the shaft and bearing are massive.
Many operations in the steel making process require large and massive shafts which rotatably support a steel or iron containing vessel. For example, a basic oxygen furnace (BOF) used in steel making includes a vessel into which scrap iron is placed and molten iron is poured for decarbonization by oxidation. When a particular quality of steel is achieved through oxidation of carbon and the addition of any desired constituent, the BOF vessel is tilted and steel is poured from the vessel into a ladle. The steel is subsequently poured from the ladle to form ingots of steel.
The BOF vessel is in essence a very large vat which is mounted for rotation on a pair of shafts. The weight of a typical empty vat is 150 tons and when filled with a charge (molten iron) such a vat plus charge will typically exceed 400 tons in weight.
A typical vessel is mounted for rotation on a pair of trunnion bearings which allow the BOF vessel to be rotated 360 degrees about a horizontal axis. When an appropriate carbon concentration in the molten metal is reached the BOF vessel is rotated approximately 180.degree. so that the molten steel can be poured into one or more ladles. The vessel is then returned to an upright position and the ladle removed from beneath the vessel. A certain amount of slag or waste remains in the bottom of the vessel. The vessel is therefore subsequently rotated 180.degree. in an opposite direction to dump the slag into a second container which removes the slag from the BOF station.
As the BOF vessel is rotated under action of a motor, the trunnion bearings in which the vessel is mounted are subject to extreme environmental conditions. As noted above, the combined weight of the vessel and its charge is typically over 400 tons and therefore significant forces are transmitted to the trunnion bearings. The extreme temperature variations in the BOF vessel cause the vessel shaft to expand and contract and thereby impart a transverse force to the BOF bearing. Other adverse environmental conditions such as dust, dirt and water also contact the BOF trunnion bearing during the steel making process.
Due to the weight and thermal expansion forces transmitted from the shaft to the bearings, the trunnion bearings can fail. It is important that an impending failure is sensed before a catostrophic accident results. Should a trunnion bearing be allowed to fail, it is possible that at some time the whole vessel could be dislodged. If this should occur when a charge is located in the vessel, molten steel would pour unchecked upon the BOF site with loss of production and damage to that site. It is therefore imperative that the condition of the BOF trunnion bearings be monitored so that maintenance and/or replacement are instituted at the first sign of failure.
The prior art technique for monitoring trunnion bearing failure was to make a physical inspection of the two trunnion bearings of each BOF vessel every two years. During an inspection if a condition was found which would indicate that a failure might occur in a short period of time, the bearing would either be replaced or serviced.
This inspection every two years technique for monitoring trunnion bearing failure, however, is based upon the premise that the bearing failure is a slow process which will take at least two years to occur. This need not be the case. If the trunnion bearing failure occurs in less than two years the inspection every two year process will not be adequate.
The periodic inspection technique for locating failures is also inefficient. By inspecting every two years, considerable time and production is lost since in most instances no wear problems are observed. While it is clear that monitoring of a BOF trunnion bearing is a necessity it is also clear that known techniques for detecting imminent failure are excessively time consuming and inadequate.